Cutting or slitting rubberized tire fabric sheet material is a difficult task. The tire fabric has parallel steel or fabric cords embedded in uncured rubber. Such sheets are continuously bias cut to form sections for building a tire carcass. The blades must be forced together at relatively high pressures. The steel or fabric cords are made of multiple strands to provide the required strength in tire carcasses. Cords may, for example, be made with multiple thin or small diameter strands of nylon, polyester or aramide fiber. Steel cords, made from multiple thin or small diameter steel wire, are extensively used. Sheets reinforced with steel cord are usually the most difficult to cut or slit and cause the most rapid wear on overlapping cutting blades. High speed steel blades have been extensively used. To improve the performance of tires, manufacturers have begun to employ high tensile wire for the steel cord. The high tensile wire has a higher hardness than previously used steel wire. As a consequence of the higher hardness, the life of overlapping cutting blades has been reduced because of the more rapid wear. The more frequent sharpening obviously increases the cost of slitting or cutting.
Efforts to employ rotary blades with overlapping offset tungsten carbide cutting edges, while providing edges with higher hardness, have not been successful in providing longer useful life. The contacting blades chip because they are more brittle than tool steel. Efforts employing a square cut blade of tungsten carbide with an overlapping square cut tool steel caused rapid wear of the tool steel blade.
It would be desirable, and it is an object of this invention to provide overlapping cutting blades with improved, longer useful life and thus reduce the costs involved in resharpening the blades.